Smoke generated by fire is one of aerosols, and is an air mass containing fine particles generated by incomplete combustion. Generally, smoke generated when combusting a substance containing cellulose (carbohydrate that makes up a third of natural vegetable materials and exists in the largest amount on earth), such as wood and paper, as a major ingredient often has a white color. The white smoke tends to generate in the early phase of fire, for example. It is important from the viewpoint of disaster prevention to early detect the white smoke generated in the early phase of fire and lightly dispersed into the air.
PTL 1 discloses a detection device that detects that smoke is generated, by performing image processing of an image captured with a camera (captured image). The detection device described in PTL 1 has configuration for calculating predetermined two or more smoke detection determination elements in a predetermined detection region in the captured image. The detection device detects that smoke is generated using the calculated smoke detection determination elements. Furthermore, the detection device has configuration for detecting that the smoke is black smoke, and has a function to issue an alarm when detecting that black smoke may be generated. Furthermore, the detection device determines breakout of fire based on the number of times of continuous detection of smoke or the like, and has a function to issue a warning when determining that fire breaks out.
NPL 1 discloses a technique for removing fog and mist from a captured image. Furthermore, the following is described in NPL 1. More specifically, when a real scene (actual landscape or the like) is captured by a camera, observation light captured with the camera is mixed light in which reflected light and environment light are mixed. The term reflected light here is light reflected by a captured object. The environment light is indirect light diffused (scattered) by objects, atmosphere, and the like.
The intensity (brightness) I of the observation light can be expressed as the formula (1).I=(1−ω)×J+ω×A  (1)
Here, in the formula (1), J represents the intensity (brightness) of the reflected light, and A represents the intensity (brightness) of the environment light. The intensity A of the environment light can be calculated by a calculation method that is not described here. In addition, w represents a superimposing rate of the environment light (a rate of the environment light included in the observation light). When smoke appears in the captured image, the superimposing rate w of the environment light becomes a higher value compared to when smoke does not appear, or an image region in which smoke does not appear. Accordingly, the superimposing rate w is evaluated using the observation light captured by the camera, and it is determined that smoke is generated (appears) when the superimposing rate w exceeds a threshold value.